Description

A simple multiplicative reflection model due to Tahir Yaqoob.

xshrefl Parameters

This model gives the reflected X-ray spectrum from a cold, optically thick, circular slab with inner and outer radii Ri and Ro respectively, illuminated by a point source a height H above the centre of the slab. The main difference between this and other reflection models is that analytic approximations are used for the Chandrasekar H functions (and their integrals) and ELASTIC SCATTERING is assumed (see Basko 1978, ApJ, 223, 268). The elastic scattering approximation means that the model is ONLY VALID UP TO ~ 15 keV in the source frame. Future enhancements will include fudge factors which will allow extension up to 100 keV. The fact that no integration is involved at any point makes the routine very fast and particularly suitable for generating error contours, especially when fitting a large number of data channels.The model is multiplicative so can be used with ANY incident continuum.

Suppose the incident photon spectrum is N(E) photons/cm/cm/s/keV and that the incident continuum is steady in time and further that the reflected continuum from the slab is R(E). When you multiply the incident spectrum with HREFL, what you actually get is

model(E) = Escfrac * N(E) + covfac * R(E)

Thus, the actual physical situation described above corresponds to Escfrac=1.0 and covfac=1.0. You may decide to float Escfrac and/or covfac. In that case, you must decide for your particular case what the best-fitting values of these parameters mean physically. It may imply time-lags between the direct and reflected components, different source and/or disk geometries to those assumed or something else.

This information is taken from the XSpec User's Guide. Version 11.3.1 of the XSpec models is supplied with CIAO 3.2.